The present invention relates to a method of and apparatus for making battery grids, and in particular to an improved method and apparatus for manufacturing battery grids in a single molding die.
Present day battery grids are often made of plastics material which acts as a mechanical frame to hold lead oxide paste, and are provided with a conductor for contacting the paste. Such grids frequently are used in automobile batteries, and when pasted are called battery plates. Lead is commonly used as the conductor since it is relatively insoluble in sulfuric acid which serves as the electrolyte, and is normally alloyed with calcium or antimony for rigidity, as pure lead is relatively soft. Other metals that are good conductors, such as copper, are soluble in sulfuric acid and would poison a lead acid battery.
As is well known, the grid generally comprises a rectangular frame formed with rectangular openings and a laterally projecting lead lug on its periphery, connected to the conductor, by means of which a plurality of grids of similar polarity may be fused together or otherwise electrically connected in parallel as by a bar leading to a battery post.
Normally, the plastics grid with conductor and lead lug is further manufactured by pasting the individual grids with a paste of lead oxide containing some sulfuric acid. These pasted grids are then dried and later subjected to an electrical charge while in sulfuric acid, whereby one group of plates called the negative plates have their lead oxide converted to lead, and another group of plates called the positive plates have their lead oxide converted to lead dioxide. A series of plates is then placed in a cell with alternating negative and positive plates and with a separator between each plate of, for example, fluted wood, perforated rubber, or the like. The battery is then filled with a dilute solution of sulfuric acid.
A cell may comprise any number of plates, with the positive plates being connected in parallel and the negative plates being connected in parallel, so that the entire cell has a desired amperage rating. In a lead oxide battery, the cell typically exhibits a voltage of approximately 2.1 volts, and depending on the desired voltage of the battery the requisite number of cells are connected in series, for example 6 cells connected in series for a 12-volt battery.
In the manufacture of battery grids, various techniques have heretofore been sued to form the conductor on the plastics lattice or frame. For example, the plastic frame and a lead grid in the shape of the conductor may separately be made, and the grid set into recesses formed in the frame to define the conductor. Or the lead grid may directly be embedded into the plastics frame in a molding process or, conversely, the frame may be joined with the lead grid by laminating, inserting or other means. Any of these previous manufacturing techniques require several separate and distinct steps for implementation, and therefore are time consuming and costly.
Once a battery grid is fabricated, the aforementioned further manufacturing thereof to produce a battery plate is ordinarily performed by automatic process. The grid is transported sequentially through various stations whereat operations performed thereon (i.e. pasting, drying, etc.) result in the battery plate. To facilitate support of the grids during transport, the grids often are formed in pairs joined by severable plastics legs, with the lead lugs of the grids extending outward from opposite sides of the pair. The grids are then supported by the lead lugs during transport between and through the manufacturing stations. Unfortunately, the lead lugs are relatively soft, and may deform in supporting the grids, particularly when the weight of the lead oxide paste is added thereto. Further, where the lugs are formed by extrusion, their positioning on opposite sides of the pair of grids requires lengthy sprues, so that a significant amount of lead remains in the sprues which must be broken off, remelted and reused.